No knock then 3 degrees pulled?

[hardcorandy]

Starting to get a little ticked off with tuning. Took the car to the track and was let down with a 107 trap speed. My tune was pretty much 11.5AFR, 11* peek timing at 23psi on my my Tdo5h 20g. Had a chat with a guy that was trapping 107 @20psi on a E316g. He told me that 11.5AFR is a little lean for pump. Add fuel and timing is what was suggested.

I change the tune to 10.5-10.8AFR and was able to hit peek timing of 16* @ 5500rpm, making sure i have a nice ramp of timing along the way. I did a few 3rd gear pulls with ZERO knock. Figuring i have it dialed in i do a 3-4 pull. No knock in third and 3* of knock about a half a second into 4th. I tried the pull again and it results in no knock. When i do get knock its all random really. Never the same exact RPM or pattern.

Does anyone have an idea of whats going on? would it be phantom or something in the tune? Do i need to worry?

 

[delta448]

It could be phantom. Try out a tank of 100+ octane.

If that cures the knock then it's not phantom and you should try lowering timing a degree or two across the board over the upper load portions. Sometimes when you're running too close to the knock limit it will show up intermittently like that. Once you cross over and hit knock, it becomes more likely to knock again on the next combustion event, even if the cells you're transitioning into have safe AFR and timing.

Another possibility is that the MAS has a small flat spot in it's response curve. If that were the case, you'd probably see the knock at roughly the same mass airflow hertz every time it decides to show up. It also may not show up as much of a lean spike on the wideband in the log depending on the sensor response time and datalogging rate.

 

[snowborder714]

Do you have any logs showing this?

 

[hardcorandy]

Makes sense Delta. Ill post logs after work today Snowboarder. Stay tuned. Thanks guys

 

[killercolt]

Was your 11.5:1 afr knocking? How much count?

 

[hardcorandy]

OK. So the "first pass" log is from the track friday night. Its not my tune currently but more or less an example of the 4th gear knock. The "16 degrees" log is the current tune. I dont have a 4th gear pull in the log but its the same deal as the track pass.

 

[DJ23GSX]

How accurate is the boost in these logs? Your timing looks a bit too aggressive to me while the turbo is spooling. Actually it looks like your timing curve is backwards in your 1st pass log. It starts pretty high at the beginning of every gear and gradually goes down by the end of it. The timing curve should start low and gradually raise as you build boost.

I've been battling a similar issue. I could make a good 3-4 3rd gear pulls with no knock and good a/f ratio's but after that I start getting random spurts of knock around 4.5k rpm's that I couldn't tune out. Since I don't have dsm link and control of timing I tried lowered my base timing to roughly 3* and last time out I made about 7-8 hard 3rd and 4th gear pulls with no more knock. In my last 2 1g's I've noticed that it was aggressive timing that was causing my knock problems rather than a/f ratio's. My only guess is after a few hard pulls the combustion chamber is getting hot and can't handle the same amount of timing it could when it was cooler.